Apache Tomcat Development

SSI How To

Table of Contents

Introduction

SSI (Server Side Includes) are directives that are placed in HTML pages,
and evaluated on the server while the pages are being served. They let you
add dynamically generated content to an existing HTML page, without having
to serve the entire page via a CGI program, or other dynamic technology.

Within Tomcat SSI support can be added when using Tomcat as your
HTTP server and you require SSI support. Typically this is done
during development when you don't want to run a web server like Apache.

Tomcat SSI support implements the same SSI directives as Apache. See the
Apache Introduction to SSI for information on using SSI directives.

SSI support is available as a servlet and as a filter. You should use one
or the other to provide SSI support but not both.

Servlet based SSI support is implemented using the class
org.apache.catalina.ssi.SSIServlet. Traditionally, this servlet
is mapped to the URL pattern "*.shtml".

Filter based SSI support is implemented using the class
org.apache.catalina.ssi.SSIFilter. Traditionally, this filter
is mapped to the URL pattern "*.shtml", though it can be mapped to "*" as
it will selectively enable/disable SSI processing based on mime types. The
contentType init param allows you to apply SSI processing to JSP pages,
javascript, or any other content you wish.

By default SSI support is disabled in Tomcat.

Installation

CAUTION - SSI directives can be used to execute programs
external to the Tomcat JVM. If you are using the Java SecurityManager this
will bypass your security policy configuration in catalina.policy.

To use the SSI servlet, remove the XML comments from around the SSI servlet
and servlet-mapping configuration in
$CATALINA_BASE/conf/web.xml.

To use the SSI filter, remove the XML comments from around the SSI filter
and filter-mapping configuration in
$CATALINA_BASE/conf/web.xml.

Only Contexts which are marked as privileged may use SSI features (see the
privileged property of the Context element).

Servlet Configuration

There are several servlet init parameters which can be used to
configure the behaviour of the SSI servlet.

expires - The number of seconds before a page with SSI
directives will expire. Default behaviour is for all SSI directives to be
evaluated for every request.

isVirtualWebappRelative - Should "virtual" SSI directive
paths be interpreted as relative to the context root, instead of the server
root? Default false.

inputEncoding - The encoding to be assumed for SSI
resources if one cannot be determined from the resource itself. Default is
the default platform encoding.

outputEncoding - The encoding to be used for the result
of the SSI processing. Default is UTF-8.

allowExec - Is the exec command enabled? Default is
false.

Filter Configuration

There are several filter init parameters which can be used to
configure the behaviour of the SSI filter.

contentType - A regex pattern that must be matched before
SSI processing is applied. When crafting your own pattern, don't forget that a
mime content type may be followed by an optional character set in the form
"mime/type; charset=set" that you must take into account. Default is
"text/x-server-parsed-html(;.*)?".

expires - The number of seconds before a page with SSI
directives will expire. Default behaviour is for all SSI directives to be
evaluated for every request.

isVirtualWebappRelative - Should "virtual" SSI directive
paths be interpreted as relative to the context root, instead of the server
root? Default false.

allowExec - Is the exec command enabled? Default is
false.

Directives

Server Side Includes are invoked by embedding SSI directives in an HTML document
whose type will be processed by the SSI servlet. The directives take the form of an HTML
comment. The directive is replaced by the results of interpreting it before sending the
page to the client. The general form of a directive is:

<!--#directive [parm=value] -->

The directives are:

config - <!--#config timefmt="%B %Y" -->
Used to set the format of dates and other items processed by SSI

echo - <!--#echo var="VARIABLE_NAME" -->
will be replaced by the value of the variable.

exec - Used to run commands on the host system.

include - <!--#include virtual="file-name" -->
inserts the contents

flastmod - <!--#flastmod file="filename.shtml" -->
Returns the time that a file was lost modified.